Evaporation of waters containing various solutes has become routine in many industrial operations. For example, evaporative based water treatment systems are now widely used for treatment of cooling tower blowdown, whether in electric power generation operations or in other industrial facilities. Also, the treatment of produced waters in oil and gas production, including production of oil from tar sands or other heavy oils, is necessary in order to condition such waters for discharge or for reuse. In some heavy oil recovery operations, the treatment of produced waters through the use of evaporators has become routine, resulting in the production of distillate that is subsequently sent to steam generators which generate steam for downhole use in the further production of heavy oil. Various types of steam generators produce steam at various pressures, but in any event, as steam generation pressures increase, the sensitivity of the steam generators to the presence of silica in feedwaters is heightened. Increased silica levels generally require increased steam generator blowdown rates, or result in increased operational costs of anion exchange equipment, or both. To avoid such costs and related operational problems, it would be desirable, when using evaporation equipment for the treatment of waters containing undesirable contaminants, and particularly when treating waters having therein somewhat volatile contaminants such as silica, to provide a method to minimize presence in evaporator distillates of such undesirable solutes, recognizing that undesirable solutes are normally present at least to some limited degree in the evaporating vapor stream within evaporation equipment.
Further, it would be desirable to provide an apparatus for reduction of the carryover of such undesirable volatile contaminants in evaporation systems. When silica (SiO2) is present at a high concentration (for example, as a percent of total brine) in an evaporation system, it will polymerize into an amorphous species having relatively high molecular weight. In the temperature range of normal operation in water treatment evaporators, such amorphous species have essentially no vapor pressure. However, when silica (SiO2) is present at a low concentration in a feedwater stream (for example, in the parts per million range), a significant portion of such silica present in the feedwater will not polymerize. A problem arises since silica molecules (SiO2) have a small vapor pressure in the normal operating temperature range of wastewater treatment evaporators. Therefore, volatile silica represents a small portion of the vapor generated by evaporation of water in such evaporators. Therefore, it would be desirable to address the problem of contamination of evaporator distillates by such volatile silica in wastewater evaporators. It would be especially desirable to address and resolve such problems when evaporators are used to treat produced waters in heavy oil production (especially tar sands production), and thus significantly minimize or avoid the resultant contamination of evaporator distillate in such operations.